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Local Group Dwarf Elliptical Galaxies: II. Stellar Kinematics to Large Radii in NGC 147 and NGC 185

Geha, M. and van der Marel, R. P. and Guhathakurta, P. and Gilbert, K. M. and Kalirai, J. and Kirby, E. N. (2010) Local Group Dwarf Elliptical Galaxies: II. Stellar Kinematics to Large Radii in NGC 147 and NGC 185. Astrophysical Journal, 711 (1). pp. 361-373. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20190510-120908598

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Abstract

We present kinematic and metallicity profiles for the M 31 dwarf elliptical (dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most extensive spectroscopic radial coverage for any dE galaxy, extending to a projected distance of 8 half-light radii (8r_(eff) ~ 14'). We achieve this coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442 member red giant branch stars in NGC 147 and NGC 185, respectively. In contrast to previous studies, we find that both dEs have significant internal rotation. We measure a maximum rotational velocity of 17 ± 2 km s^(–1) for NGC 147 and 15 ± 5 km s^(–1) for NGC 185. While both rotation profiles suggest a flattening in the outer regions, there is no indication that we have reached the radius of maximum rotation velocity. The velocity dispersions decrease gently with radius with average dispersions of 16 ± 1 km s^(–1) and 24 ± 1 km s^(–1) for NGC 147 and NGC 185, respectively. The average metallicities for NGC 147 and NGC 185 are [Fe/H] = –1.1 ± 0.1 and [Fe/H] = –1.3 ± 0.1, respectively; both dEs have internal metallicity dispersions of 0.5 dex, but show no evidence for a radial metallicity gradient. We construct two-integral axisymmetric dynamical models and find that the observed kinematical profiles cannot be explained without modest amounts of non-baryonic dark matter. We measure central mass-to-light ratios of M/L_V = 4.2 ± 0.6 and M/LV = 4.6 ± 0.6 for NGC 147 and NGC 185, respectively. Both dE galaxies are consistent with being primarily flattened by their rotational motions, although some anisotropic velocity dispersion is needed to fully explain their observed shapes. The velocity profiles of all three Local Group dEs (NGC 147, NGC 185, and NGC 205) suggest that rotation is more prevalent in the dE galaxy class than previously assumed, but often manifests only at several times the effective radius. Since all dEs outside the Local Group have been probed to only inside the effective radius, this opens the door for formation mechanisms in which dEs are transformed or stripped versions of gas-rich rotating progenitor galaxies.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1088/0004-637x/711/1/361DOIArticle
https://arxiv.org/abs/0911.3654arXivDiscussion Paper
ORCID:
AuthorORCID
Geha, M.0000-0002-7007-9725
van der Marel, R. P.0000-0001-7827-7825
Guhathakurta, P.0000-0001-8867-4234
Gilbert, K. M.0000-0003-0394-8377
Kalirai, J.0000-0001-9690-4159
Kirby, E. N.0000-0001-6196-5162
Additional Information:© 2010. The American Astronomical Society. Received 2009 July 30; accepted 2010 January 6; published 2010 February 10. We thank S. Demers and P. Battinelli for kindly providing their photometric catalogs before publication. We also kindly thank Michael Rich for sharing Keck observing time with part of this project. Support for this work was provided in part by NASA through Hubble Fellowship grant HST-HF-01233.01 awarded to E.N.K. by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract NAS 5-26555.
Funders:
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF-01233.01
NASANAS 5-26555
Subject Keywords:galaxies: dwarf; galaxies: individual (NGC 147 NGC 185) ; galaxies: kinematics and dynamics
Issue or Number:1
Record Number:CaltechAUTHORS:20190510-120908598
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190510-120908598
Official Citation:M. Geha et al 2010 ApJ 711 361
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95410
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:10 May 2019 21:29
Last Modified:06 Nov 2019 23:01

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